Sensor placement for irrigation scheduling in banana using ... - UFRB

18Silva et al.q (k + 2)- soil water content immediately beforethe following irrigation, m 3 m -3The concentration limits for the roots ofbanana plant have been established based on theknowledge of the effective root depth (ERD) andalso the effective root distance (ERDi), with “EDR”being defined as the depth that contains 80%of total root length and “ERDi” as the distancethat contains 80% of the total root length. Acharacterization of the effective extraction depth(EED) and the effective extraction distance (EEDi)was made based on the knowledge of the zonewhere most of root activity occurs. The effectiveextraction depth (EED) corresponded to the regionof the soil profile, starting from the soil surface,where at least 80% of the total water is extractedby roots and EEDi corresponded to the region ofthe soil profile from the plant, where at least 80%of the water is also extracted by the roots. Thepercentages of soil available water were establishedat each location of the profile (R, Z), based on thesoil water characteristic curve by Eq. (4):⎛ θ( RZ , )− θAD( RZ , )=⎜⎝ θcc− θpmppmp⎞⎟ × 100⎠where:AD(R, Z) - percentage of available water at apoint (R, Z) in the soil profileq(R, Z) - soil water content at a point (R, Z) ofthe soil profile, m 3 m -3q pmp- soil water content referring to permanentwilting point, m 3 m -3q cc- soil water content referring to fieldcapacity, m 3 m -3Percolation loss, DP (R, Z R) can be calculatedby Eq. (5) for each distance R just below theeffective depth of the roots, Z Rthat was assumedas 0.9 m:DP( RZ , )=Rk+2∫k+1qdtwhere:k + 1 - time when soil water content reachedits maximum value at shallow locations (R, Z) andthe wetting front reached the depth of 0.9 mk + 2 - time of the next irrigationθt− θtq = + 1∆t(4)(5)(6)where:Dt - time interval, 1 hq - flow of water, cm 3 h -1 , in 1 cm 3 of the soilq t- soil water content at the time tq t+1- soil water content at the time t + 1The average percolation loss in the profile, i.e,from plant to a distance R can be calculated by theEq. (7):DPm∑ DP RZ ,R=n( )where:n - number of distances (R) from the plantThe values of DPm calculated for differentmoments in time after the beginning of irrigationfor treatments T1, T2 and T3 were compared bythe least significant difference (LSD) test at aprobability level of 0.05.Results and DiscussionWater distribution and deep percolationResults showed that the largest precipitationvalues were always registered on the collectorsfurthest away from the plants and close to themicrosprinklers, and there were records ofprecipitations of 5.1, 10.2 and 5.0 mm at a distanceof 1 m, while at a distance of 0.2 m the precipitationsas observed were 1.05, 0.35 and 2.02 mm for thetreatments T1, T2 and T3, respectively (Figure 3).There was the loss of water by percolation in allstudied treatments. Table 2 presents average valuesof percolated water depths at different momentsafter the beginning of irrigation for treatments T1, T2and T3. By comparison of the means for treatmentsat specific times, the values of the percolatedwater depths varied significantly based on theconfigurations of the irrigation systems, tested up to1 hour after the start of irrigation and, after 2 and 4hours the means were different and only higher inthe case of treatment T2. There were no significantdifferences in the mean percolated water depthvalues between 6 and 14 h after the start of irrigation.Root distributionThe isolines of distribution of root lengthdensity in the soil profile and also the percentageof cumulative root length in the soil profile athorizontal distances towards the microsprinklerand depths are shown in Figures 4 and 5. Theeffective root depths in case of a microsprinklerof 32 L h -1 for four plants (T1), a microsprinkler of60 L h -1 for four plants (T2) and a microsprinklerR(7)Water Resources and Irrigation Management, v.1, n.1, p.15-23, 2012.